Traffic signal lights have been around for years and are used to efficiently control traffic through intersections. While traffic signals have been around for years, improvements continue to be made in the areas of traffic signal light control algorithms, traffic volume detection, and emergency vehicle detection.
The current state of the art for solid state light sources is as direct replacements for incandescent light sources. The life time of traditional solid state light sources is far longer than incandescent light sources, currently having a useful operational life of 10–100 times that of traditional incandescent light sources. This additional life time helps compensate for the additional cost associated with solid state light sources.
One problem with traditional light sources for traffic signals is detection of the light output using the traditional hand held meter. Ambient light greatly affects the accurate detection of light output from the light source. Therefore, it has been difficult in the past to precisely set the light output to a level that meets DOT standards, but which light source is not over driven to the point of providing more light than necessary, which as previously mentioned, increases temperature and degrades the useful life of the solid state device. One conventional approach is to mount an ambient light sensor near the outer edge of the traffic signal lens cover. However, this design necessitates additional machining due to the additional complexity of the signal light cover, and the need for an additional mounting assembly for the sensor that also uses up valuable space.
There is desired an improved ambient light sensing apparatus and methodology which is less complex, occupies less space and which is not disturbed by the light output of the light source.